High-strength aluminum-magnesium silicon alloy and manufacturing process thereof

ABSTRACT

A high-strength aluminum-magnesium silicon alloy and its manufacturing process which includes a composition adjusting step to add vanadium (V) and zirconium (Zr) in an aluminum-magnesium silicon alloy to refine grains of the alloy; a material casting step, a material preheating step, a hot forging step and a heat treatment step to melt magnesium and silicon atoms into an aluminum base to cause a lattice distortion and achieve a strengthening effect and precipitate Mg 2 Si from the grains of the alloy, and the precipitated particles act as obstacles to dislocation movement. Therefore, the alloy product has a yield strength improved by 31%, the ultimate strength by 39%, the hardness by 34%, and the fatigue strength by 55%. Therefore, the alloy product can be used in components with a high strength requirement such as the aluminum alloy wheels and the control arms of a car suspension system.

FIELD OF THE INVENTION

The present invention relates to a high-strength aluminum-magnesiumsilicon alloy, and more particularly to the technical area of improvingthe strength, hardness and fatigue resistance of an alloy product byadjusting the composition of trace elements of an alloy material andprocessing the alloy material with hot forging and heat treatment.

BACKGROUND OF THE INVENTION

As science and technology advance, aluminum alloys with the features oflight weight, high corrosion resistance, easy molding and manufacture,high electric conductivity, high thermal conductivity and nontoxicityhave been used extensively in different industries. Referring to theChinese National Standards (CNS) and U.S. Aluminum Industry Standards,forged alloys can be divided into AA1xxx series pure aluminum, AA2xxxseries aluminum-copper alloys, AA3xxx series aluminum-manganese alloys,AA4xxx series aluminum-silicon alloys, AA5xxx series aluminum-magnesiumalloys, AA6xxx series aluminum-magnesium silicon alloys and AA7xxxseries aluminum-zinc-magnesium alloys, etc.

In the aforementioned alloys, the AA6xxx series alloys can achieve aprecipitation strengthening effect by adding a trace amount of magnesium(Mg) and silicon (Si) elements. The strength of the AA6xxx series alloysis moderate among these alloys, but the formability, acid resistance,weldability, and anodic treatment effect are very good, so that theAA6xxx series alloys are used extensively by manufacturers, and thecommon ones include the AA6053, AA6061, AA6063 and AA6151 alloys.

With reference to FIGS. 10 and 11, the AA6061 alloy generally has achemical composition including 0.579 wt. % silicon (Si), 0.62 wt. % iron(Fe). 0.261 wt. % copper (Cu), 0.103 wt. % manganese (Mn), 1.024 wt. %magnesium (Mg), etc., and the AA6061 alloy ingot has grains with anaverage size or diameter of 125 μm (as shown in FIG. 12). Although thestrength of the AA6061 alloy is incomparable with the strength of theAA2xxx series alloys and the AA7xxx series alloys, and the AA6061 alloyhas better manufacturability, formability, weldability and corrosionresistance, and its extrusion speed is three to four times of theextrusion speed of the AA5056 alloy. Therefore, the alloy forging costof the AA6061 alloy is lower than the alloy forging cost of the AA2xxxseries alloys and the AA7xxx series alloys. In addition, the AA6061alloy processed by T6 heat treatment can obtain excellent mechanicalproperties including a yield strength up to 275 MPa, an ultimatestrength up to 310 MPa, a Brinell hardness of 95 HBW, and a fatiguestrength of approximately 96.5 MPa, etc. Since the construction materialof the AA6061 alloy is lighter than the foregoing ones, therefore theAA6061 can be applied extensively in key components of means oftransportation such as bicycles, cars, ships and airplanes. As theultimate strength, hardness and fatigue resistance are importantmechanical properties of a construction material, how to obtain the bestmechanical properties of an aluminum-magnesium silicon alloy in whatevercondition is a subject worth researching. For instance, a high strengthAl—Mg—Si alloy as disclosed in U.S. Pat. No. 5,571,347 achieves theeffect of increasing the ultimate strength and the yield strength of analloy material up to 434 MPa and 379 MPa respectively by changing thecomposition of the material, adding more magnesium (Mg) and silicon (Si)elements in melting aluminum ingots, and producing solid solution andaging strengthening effects by T6 heat treatment. Since beryllium (Be)and its compound have a relatively greater toxicity and a relativelyhigher risk in melting, therefore the present invention eliminates theaddition of beryllium (Be). Further, an aluminum alloy having improveddamage tolerant characteristics as disclosed in U.S. Pat. No. 5,888,320achieves the effect of increasing the ultimate strength and the yieldstrength of an alloy material up to 403 MPa and 367 MPa respectively bychanging the composition of the material, adding more copper element(such as 0.88 wt %) when melting an aluminum alloy, and producing solidsolution and aging strengthening effects by T6 heat treatment.

SUMMARY OF THE INVENTION

Therefore, it is a primary objective of the present invention to providea high-strength aluminum-magnesium silicon alloy with better strength,hardness and fatigue resistance than the present existingaluminum-magnesium silicon alloys and to further provide a manufacturingprocess of the high-strength aluminum-magnesium silicon alloy.

To achieve the aforementioned objective, the present invention improvesthe mechanical properties including the strength, hardness and fatigueresistance of an aluminum-magnesium silicon alloy by adjusting thecomposition of an alloy material, and setting the heat treatmentparameters. In the aspect of adjusting the composition, trace elementssuch as vanadium (V) and zirconium (Zr) are added into thealuminum-magnesium silicon alloy to perform a grain refinement of thematerial in order to improve the strength of an alloy product of thepresent invention. In the composition of the alloy material of thepresent invention, the trace elements including 0.4˜1.2 wt. % silicon(Si), less than 0.7 wt. % iron (Fe), 0.2˜1.0 wt. % copper (Cu), lessthan 0.2 wt. % manganese (Mn), 0.6˜1.6 wt. % magnesium (Mg), less than0.2 wt. % zinc (Zn), less than 0.10 wt. % titanium (Ti), 0.05˜0.3 wt. %chromium (Cr), 0.1˜0.5 wt. % vanadium (V), 0.1˜0.5 wt. % zirconium (Zr)and less than 0.15 wt. % of impurity are added into the main materialaluminum (Al).

The alloy heat treatment of the present invention comprises thefollowing steps: (a) Solution treatment step, wherein a finished good isput into a solution furnace heated to a temperature of 530˜580° C. andheld at the temperature for 1˜3 hours; (b) Quenching treatment step,wherein the finished good processed by the solution treatment isimmersed into a quenching liquid of 50˜70° C. for a quenching treatmenttime of 15˜45 minutes; and (c) Aging treatment step, wherein theproduced processed by the quenching treatment is put into an agingfurnace and heated to 160˜180° C. and held at the temperature for 14˜18hours.

After the aforementioned three steps are completed, the finished good iscooled by air to form an alloy product with a better strength.

In addition, the following steps of the present invention can also beused to obtain the alloy product of the invention: (a) Alloy compositionadjusting step as described above; (b) Material casting step, whereinthe foregoing molten alloy composition is casted and molded into amaterial; (c) Material preheating step, wherein the material ispreheated before forging, and the material is put into a preheatingfurnace heated to a temperature over 500° C. and held at thattemperature for at least two hours; (d) Forging molding step, wherein amold is heated to 200˜400° C., and the operating temperature for forgingis set within a range of 250˜500° C., and the material is forged to forma product; and (e) Heat treatment step as described above, wherein theproduct is processed by a solution treatment, a quenching treatment andan aging treatment sequentially, and finally air cooled to form an alloyproduct of the present invention.

In summation, the present invention adopting the aforementionedtechnical measures has the following advantages and effects:

The present invention adds the trace elements including vanadium (V) andzirconium (Zr) into an aluminum-magnesium silicon alloy to refine thegrains of the material to a diameter from 50 μm to 100 μm and thusreducing the grain size by 20% over the grain size of the AA6061 castingot to improve the mechanical properties of the subsequent alloyproduct.

The material of the present invention is hot forged and molded, and thena solution heat treatment is performed to melt magnesium (Mg) andsilicon (Si) atoms into an aluminum (Al) base to result in a latticedeformation and achieve a strengthening effect, and then an aging heattreatment is performed to precipitate (Mg₂Si) from grains in aprecipitated phase, and the precipitated particles act as obstacles todislocation movement, so that the alloy product of the present inventionhas a yield strength up to 400 MPa, an ultimate strength up to 505 MPa,a Brinell hardness of 127.3 HBW and a fatigue strength of 155 MPa.Compared with the AA6061-T6, the present invention increases the yieldstrength of the alloy product by 31%, the ultimate strength by 39%, thehardness by 34%, and the fatigue strength by 55.4%, so that the alloyproduct of the invention can be used in components with a highstructural strength requirement, such as aluminum bicycle frames andframe tubes, aluminum alloy wheels, control arms of a car suspensionsystem as well as alloy products of the transportation means industry,mechanical tool industry, national defense and weapon industry,aerospace industry, 3C electronic industry, and sports and leisure goodsindustry.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 is a flow chart of manufacturing a high-strengthaluminum-magnesium silicon alloy of the present invention;

FIG. 2 is a list of trace elements contained in a material of thepresent invention;

FIG. 3 is the microstructure of the center of a material of the presentinvention;

FIG. 4 is the microstructure of the edge of a material of the presentinvention;

FIG. 5 is a list showing the values of yield strength, ultimate strengthand elongation of a material of the present invention;

FIG. 6 is a list showing the value of Brinell hardness of a material ofthe present invention;

FIG. 7 is a flow chart of a heat treatment step of an alloy product ofthe present invention;

FIG. 8 is a list showing the values of yield strength, ultimate strengthand elongation of an alloy product of the present invention;

FIG. 9 is a list showing the value of Brinell hardness of an alloyproduct of the present invention;

FIG. 10 is a list of trace element contents of a conventional AA6061alloy;

FIG. 11 is a list of mechanical properties of a conventional AA6061alloy processed by heat treatment; and

FIG. 12 is the microstructure of an AA6061 material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The technical characteristics, contents, advantages and effects of thepresent invention will be apparent with the detailed description of apreferred embodiment accompanied with related drawings as follows.

With reference to FIGS. 1 and 3 for a high-strength aluminum-magnesiumsilicon alloy and its manufacturing process in accordance with thepresent invention, the manufacturing process comprises the followingsteps: (a) an alloy composition adjusting step; (b) a material castingstep; (c) a material preheating step; (d) a hot forging step; and (e) aheat treatment step.

In the alloy composition adjusting step (a) as shown in FIGS. 3 and 4,the microstructure show whether there are too many cast holes, cracksand defects, and a better composition is chosen to satisfy the requiredmechanical properties of an aluminum-magnesium silicon alloy and enhancethe fatigue resistance effectively. In FIG. 2, the content of traceelements is adjusted and the traced elements are melted into a mainmaterial aluminum (Al).

The silicon (Si) content is 0.4˜1.2 wt. % and used for improving theflowing capability of the molten aluminum (Al), the hot-crackingresistance, the specific gravity and thermal expansion coefficient, andobtaining a solid solution strengthening effect in the subsequent heattreatment step of the present invention.

The iron (Fe) content is less than 0.7 wt. % and used for improving thehot-cracking resistance of the alloy, and achieving a grain refinementof the material of the present invention.

The copper (Cu) content is 0.2˜1.0 wt. % and used for improving thestrength and hardness of the alloy significantly, but reducing thehot-cracking resistance), and obtaining a precipitation strengtheningeffect in the subsequent heat treatment step of the present invention.

The manganese (Mn) content is less than 0.2 wt. % and controlled to alower content in the alloy for improving the tenacity of the alloy, andobtaining the solid solution strengthening effect and the precipitationstrengthening effect in the subsequent heat treatment step of thepresent invention.

The magnesium (Mg) content is 0.6˜1.6 wt. % and used for improving thestrength and hardness of the alloy processed by heat treatment, andsetting Mg₂Si mainly in a precipitated phase, and obtaining theprecipitation strengthening effect in the subsequent heat treatment stepof the present invention.

The zinc (Zn) content is less than 0.2 wt. % and used for reducingoxidation in the alloy and obtaining the precipitation strengtheningeffect in the subsequent heat treatment step of the present invention.

The titanium (Ti) content is less than 0.10 wt. % and used for a grainrefinement of the material of the present invention.

The chromium (Cr) content is 0.05˜0.3 wt. % and used for forming anintermetallic compound such as (CrFe)A₁₇ and (CrMn)Al₁₂ in aluminum,obstructing the heat treatment and hot forging re-crystallizationnucleation and growth processes to achieve a strengthening effect to acertain extent and also improve the tenancy of the alloy and lower thesensitivity to stress, corrosion, and cracking, but improve thesensitivity of the quenching treatment, and obtaining a solid solutionstrengthening effect in the subsequent heat treatment step of thepresent invention.

The vanadium (V) content is 0.1˜0.5 wt. % and capable of achieving thegrain refinement effect of the material of the present invention, andobtaining the precipitation strengthening effect in the subsequent heattreatment step of the present invention.

The zirconium (Zr) content is 0.1˜0.5 wt. % and capable of achieving thegrain refinement effect of the material of the present invention, andobtaining the precipitation strengthening effect in the subsequent heattreatment step of the present invention.

In the material casting step (b), the main material aluminum (Al) andthe aforementioned trace elements are melted together by a hightemperature into a molten state, and then degassed and slagged off, andthen casted into ingots, rods sheets, materials with a predeterminedcross-sectional shape, or materials with any shape to facilitateupstream manufactures to transport products to downstream forgingmanufactures. Due to the change of trace elements contained in thematerial, particularly those containing vanadium (V) and zirconium (Zr)elements, the grains can be refined to have a diameter from 50 μm to 100μm . With reference to FIGS. 3 and 4 for microstructure of the materialof the present invention, the grain refinement helps improving thestrength, hardness and fatigue resistance of the subsequent alloyproduct of the present invention. With reference to FIGS. 5 and 6, sixsamples of the material of the present invention are collected fortesting, and test results show that the material has an average yieldstrength of 133.66 MPa, an ultimate strength of 176.38 MPa, anelongation of 13.26 EL %, and an average Brinell hardness of 54.9 HBW.

In the forging preheating step (c), the aforementioned ingots, rods,sheets or material with a predetermined cross-sectional shape arepreferred. For example, the manufacture of a forged wheel requiresmanufacturers to put the material into a preheating furnace at atemperature of 300˜500° C. and that temperature is held for 120˜180minutes.

In the hot forging step (d), parameters for the hot forging manufactureof the material of the present invention are set. For example, the moldof a forged wheel is heated to 200˜400° C., and the operatingtemperature for the forging process is set within a range of 350˜450°C., and the forging pressurization time is set to 3 seconds, and theforging pressure is set to 55000 KN.

The material is forged into an alloy product of a predetermined shape,so that the hot forging step performs a plastic processing of thematerial to improve the grain structure of the material, and thematerial of the alloy product is reformed and homogenized. In addition,a mechanical fibrosis state caused by the continuous grain flow resultsin better mechanical properties including the fatigue resistance,tenacity, and impact resistance of the alloy product.

In the heat treatment step (e) as shown in FIG. 7, the aforementionedalloy product is put into a solution furnace and heated to a temperatureof 530˜580° C., and that temperature is held for 1˜3 hours, and then thealloy product processed by the solution treatment is immersed completelyinto warm water of 50˜70° C., and the quenching treatment time is 15˜45minutes, and then quenched alloy product is put into an aging furnaceand heated to a temperature of 160˜180° C., and that temperature is heldfor 14˜18 hours, Finally, the alloy product is air cooled to form thealloy product of the present invention. In the step (e), a solutiontreatment of the alloy product of the present invention is performed tomelt magnesium (Mg) and silicon (Si) atoms into an aluminum (Al) base tocause a lattice deformation and achieve a strengthening effect, and thenan aging heat treatment is performed to precipitate (Mg₂Si) from grainsin a precipitated phase, and the precipitated particles act as obstaclesto dislocation movement, so as to enhance the strength of the alloyproduct of the present invention.

With reference to FIGS. 8 and 9, several samples of the alloy productproduced according to the aforementioned manufacturing process of thepresent invention are collected for testing, and test results show thatthe alloy product has an average yield strength of 400.33 MPa, anultimate strength of 504.87 MPa, an elongation of 7.67 EL %, and anaverage Brinell hardness of 127.3 HBW. Compared with the general AA6061material, the material of the present invention has much higherstrength, hardness and fatigue resistance.

It is noteworthy that the alloy product of the present invention can becasted as a whole by a single production unit. In other words, thecomposition of the alloy material of the present invention is castedinto a material first, and then processed with a coherent operation ofthe aforementioned hot forging process and the heat treatment process toproduce the alloy product of the present invention, or two productionunits such as a casting factory and a forging factory located with a fardistance apart can cooperate with each other. The casting factor caststhe material into an easily transported material such as an ingot, asheets, a rod, or a material with a predetermined cross-sectional shapeaccording to Steps (a) and (b) of the manufacturing process of thepresent invention, and then delivers the material to the forgingfactory. The forging factory refers to Steps (c), (d) and (e) of themanufacturing process of the present invention to manufacture the alloyproduct of the present invention.

In summation of the description above, the high-strengthaluminum-magnesium silicon alloy and its manufacturing process inaccordance with the present invention adds vanadium (V) and zirconium(Zr) into an aluminum-magnesium silicon alloy to achieve the grainrefinement effect of the alloy and applies the solution heat treatmentto melt magnesium (Mg) and silicon (Si) atoms into an aluminum (Al) baseto cause a lattice distortion and achieve a strengthening effect andprecipitate Mg₂Si from the grains of the alloy, and the precipitatedparticles act as obstacles to dislocation movement. The alloy product ofthe present invention has a yield strength up to 400 MPa, an ultimatestrength up to 505 MPa, a Brinell hardness 127.3 of HBW, and a fatiguestrength of 155 MPa, and thus the alloy product of the present inventioncan be used in components with a high structural strength requirement,such as aluminum bicycle frames and frame tubes, aluminum alloy wheels,control arms of a car suspension system as well as alloy products of thetransportation means industry, mechanical tool industry, nationaldefense and weapon industry, aerospace industry, 3C electronic industry,and sports and leisure goods industry.

The composition of trace elements and the manufacturing process ofproducing alloys with improved strength in accordance with the presentinvention comply with the patent application requirements, and thus theinvention is duly filed for patent application. While the invention hasbeen described by means of specific embodiments, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the scope and spirit of the invention set forth in theclaims.

What is claimed is:
 1. A high-strength aluminum-magnesium silicon alloy,with a trace element composition comprising: 0.4˜1.2 wt. % silicon (Si),less than 0.7 wt. % iron (Fe), 0.2˜1.0 wt. % copper (Cu), less than 0.2wt. % manganese (Mn), 0.6˜1.6 wt. % magnesium (Mg), less than 0.2 wt. %zinc (Zn), less than 0.10 wt. % titanium (Ti), 0.05˜0.3 wt. % chromium(Cr), 0.1˜0.5 wt. % vanadium (V), 0.1˜0.5 wt. % zirconium (Zr) and lessthan 0.15 wt. % impurity which are melted with aluminum (Al) to producea material.
 2. The high-strength aluminum-magnesium silicon alloy ofclaim 1, wherein grains of the high-strength aluminum-magnesium siliconalloy are refined to a diameter from 50 μm to 100 μm to improvemechanical properties of a subsequent alloy product.
 3. A high-strengthaluminum-magnesium silicon alloy manufacturing process, comprising thesteps of: (a) an alloy melting step that melts a plurality of traceelements into a balanced amount of aluminum raw material, and the traceelements comprising: 0.4˜1.2 wt. % Si, less than 0.7 wt. % Fe, 0.2˜1.0wt. % Cu, less than 0.2 wt. % Mn, 0.6˜1.6 wt. % Mg, less than 0.2 wt. %Zn, less than 0.10 wt. % Ti, 0.05˜0.3 wt. % Cr, 0.1˜0.5 wt. % V, 0.1˜0.5wt. % Zr and less than 0.15 wt. % impurity; (b) a material casting step,wherein a molten alloy material is casted and formed into a material,and grains of the high-strength aluminum-magnesium silicon alloy arerefined to a diameter of 50 μm˜100 μm; (c) a forging preheating step,wherein the molded material is put into a preheating furnace at atemperature of 300˜500° C. and held at said temperature for at least120˜180 minutes; (d) a hot forging step, wherein a mold is heated to200˜400° C., and an operating temperature during forging is set to atemperature range of 250˜500° C., and the molded material is forged toform an alloy product; and (e) a heat treatment step, wherein a solutiontreatment, a quenching treatment, an artifical aging treatment of thealloy product are performed sequentially, and then the alloy product iscooled in air to form a high-strength aluminum-magnesium silicon alloyproduct.
 4. The high-strength aluminum-magnesium silicon alloymanufacturing process of claim 3, wherein the heat treatment step is toput the alloy product in a solution furnace heated to 530˜580° C. andmaintaining the temperature for 1˜3 hours, and then submerge the alloyproduct completely into a quenching liquid of 50˜70° C., and after aquenching treatment time of 15˜45 minutes, the quenched alloy product isput into an aging furnace heated to 160˜180° C. and maintaining thetemperature for 14˜18 hours, and then the alloy product is cooled in airto produce the aluminum-magnesium-silicon alloy product.
 5. Thehigh-strength aluminum-magnesium silicon alloy manufacturing process ofclaim 3, wherein the aluminum-magnesium silicon alloy product has ayield strength up to 400 MPa, an ultimate strength up to 505 MPa, aBrinell hardness up to 127.3 HBW and a fatigue strength up to 155 MPa.